1. Field of the Invention
The present invention relates to pneumatic drive systems for pumps and, more particularly, but not by way of limitation, to a pneumatically driven pump system positionable within a borehole to pump fluids from a well.
2. Description of the Related Art
In the absence of electrical power, windmills remain the preferred device for pumping fluids, especially water, from the ground. Windmills typically comprise a vaned wheel connected to a shaft which is supported on a frame. As the vaned wheel rotates, gears transfer the rotational force developed by the shaft to sucker rods which connect to a downhole pump. The sucker rods drive the downhole pump to pump water from the well. Windmill driven pumping systems operate adequately provided there is a sufficient amount of wind to drive the windmill's vaned wheel. However, during periods of low wind activity, the vaned wheel supplies no power to the pump, resulting in periods of water shortages.
In an attempt to provide pumping power regardless of wind activity, U.S. Pat. No. 4,358,250, issued Nov. 9, 1982 to Payne, discloses storing energy developed by the windmill during high levels of wind activity for use during low levels of wind activity. In Payne, the drive shaft of the vaned wheel connects to a compressor which compresses air and stores the compressed air for later use. The compressor delivers the compressed air to a pneumatic cylinder positioned over the borehole of the well to reciprocally drive the pneumatic cylinder. Sucker rods connect the pneumatic cylinder to a down-hole pump so that the reciprocating motion of the pneumatic cylinder drives the pump to pump water from the well. Thus, the windmill disclosed in Payne operates on a continual and constant basis because it stores energy in the form of compressed air for later use.
Unfortunately, although the Payne windmill stores energy for later use, it suffers the same disadvantages as all windmills employing an above-ground pump drive system. Specifically, when the pump drive system resides above the ground, sucker rods must be utilized to deliver the driving force of the drive system to the pump. Sucker rods typically consist of wooden rods in twenty foot sections coupled together with metal connectors. Sucker rods are impractical because they are expensive and must be replaced often. The sucker rods must be replaced often because they are wooden and, as such, rapidly deteriorate in the water. Additionally, when the sucker rods are removed to permit work on the well, they must be continually wet with water to prevent their drying out. If they dry out before their return to the well, they fall apart within the well which results in their again having to be replaced.
Furthermore, if the sucker rods become misaligned within the borehole, the metal connectors coupling them together rub against the borehole casing as the sucker rods reciprocate. The rubbing of the metal connectors against the borehole casing results in holes wearing through the casing which causes leaking. Once the casing begins to leak, it must be replaced. Unfortunately, both the borehole casing and the labor involved in replacing it are extremely expensive. Accordingly, pump drive systems positioned above-ground are high cost systems requiring significant amounts of maintenance.
U.S. Pat. No. 4,385,871, issued on May 31, 1983 to Beisel, attempts to overcome the above problems by utilizing a windmill which eliminates sucker rods. In Beisel, a windmill drives an air compressor which delivers compressed air directly into the well. The compressed air entering the well displaces the water and forces it from the well into the borehole and out an exit port from the bore hole. Although Beisel eliminates sucker rods, it is extremely inefficient and may only be employed in very shallow wells, typically 20 to 25 feet. That is, its windmill and compressor unit produce insufficient pressures within the well to drive water against the force of gravity for a distances of longer than the 20-25 feet. Thus, the Beisel device is impractical because most wells must exceed 20-25 feet in order to produce sufficient quantities of water.
U.S. Pat. No. 4,174,926, issued on Nov. 20, 1979 to Hamrick, et al., discloses a windmill that eliminates the necessity of sucker rods and, further, places the pump drive system within the well. The Hamrick, et al. system includes a propeller driven shaft which pressurizes hydraulic fluid stored within a fluid accumulator. The accumulator delivers the fluid to a turbine located downhole to drive the turbine which, in turn, drives a pump to pump water from the well.
Although the Hamrick, et al. system eliminates sucker rods, it suffers from a serious disadvantage. Specifically, the Hamrick, et al. system presents the serious problem of well contamination. If the hydraulic fluid utilized to drive the turbine leaks into the well water, it would contaminate the well, thereby making the water undrinkable. With the well contaminated with hydraulic fluid, it would have to be cleaned or possibly abandoned. In either instance, the cost to the well owner is significant. Accordingly, the Hamrick, et al. system fails to provide an adequate solution to above-ground pump drive systems because its use presents a potential health hazard.
Accordingly, a system that provides a pump drive system positioned downhole which does not utilize hydraulic fluid is highly desirable.